1. Field of the Invention
The present invention relates, in general, to a multi-pole breaker assembly, of the type adopted within the field of the so-called medium voltage distribution system for the primary stations. The present invention further relates to a method for operating a distribution system of medium voltage, in particular for primary stations, including at least one multi-pole breaker assembly.
In particular, said multi-pole breaker assembly is of the type comprising breakers, each having an insulating case developing along a prevailing direction thereof, forming the median axis of each breaker, the median axes of the breakers of said assembly being substantially parallel among them, said breakers being apt to be moved with respect to respective input and output external contact to carry out a line disconnection.
2. Description of the Prior Art
The term multi-pole breaker assembly is used to indicate an electrical apparatus that carries out both the function of breaking, i.e. the cut-off and the make of an electric circuit, in presence of the normal operating current as well as in presence of the short-circuit current.
Moreover, by moving said breakers the disconnection of the network connected thereof is also performed, for instance the disconnection of medium voltage lines outgoing from a primary station.
This type of apparatus, within the range of the so-called medium voltage (1-52 kV), uses breakers comprising a fixed internal contact and a movable internal contact, apt to interact between them to open and to close the circuit. Both the internal contacts are connected with suitable input and output conductive rods, to respective outer terminals usually arranged at the ends of the insulating case.
The assemblies of the specified type can use a wide range of breakers that are distinguishable among them for their structure and for the implied dielectric medium, wherein said internal contacts are immersed, which carry out the function of shutting off the electric discharge that is formed when a current circulates therein.
The most common medium voltage breakers are of the type: with reduced oil; with air, so-called magnetic blow out breakers; and with sulphur hexafluoride (SF6). A few years ago, and with some success, breakers wherein the separation of the internal contacts takes place in a vacuum, i.e. the so-called vacuum bottle breakers were introduced. This latter type of breakers is particularly compact, light, and allowed a reduction in the sizes of the distribution systems.
This reduction could entail obvious advantages in terms of cost-effectiveness, allowing the realisation of the abovementioned distribution system in a transportable solution and allowing the use thereof in primary stations, either in emergency situations or in stationary installations.
In a distribution system, a multi-pole breaker assembly comprises a metallic wall bay, wherein it is normally housed, and that forms a sort of cell or module of said distribution system.
The electrical insulation between the metallic walls and each breaker is ensured by the distance in air separating the two components, and specific rules do exist to provide certain insulation distances in air for electrical equipment that are therefore called air insulated, precisely to prevent the sparkling of sudden electrical arcs between the components, possibly in case of overvoltages.
Obviously, such minimum insulation distances must be kept regardless of the position of the breakers that, as aforestated, are moved to operate the steps of connecting the line, or the disconnection thereof.
Having to keep these minimum distances, the known multi-pole breaker assemblies do not permit, in said positions, to reduce the transversal dimensions of said bays of the assemblies that would allow, for instance, the creation of standardised modules of the distribution system, forming a transportable structure, suitable to various uses as a medium voltage section transportable to primary stations.
As a matter of fact, such assemblies mainly can be divided into two different categories.
Within the first category, multi-pole breaker assemblies can be found wherein the positions of connection and of disconnection of the line are carried out with an horizontal translation movement, i.e. perpendicular to said median axes. This type of assemblies has transversal dimensions that must take into account the translated positions of the set of breakers.
In the second category assemblies can be found wherein the breakers are rotated, rather than translated, around an axis of rotation substantially perpendicular to said median axes. This rotation, having to take place inside of a space internal to the bay, does not allow to optimise the sizes of the latter, particularly widthwise.
An assembly of this type is described for instance in the European Patent No. 0,543,683.